Aluminum nitride (AlN) is a III/V group semiconductor compound and a ceramic material. Aluminum nitride has a hexagonal wurtzite structure, and its nitrogen atom and aluminum atom are covalently linked to form a tetrahedral structure. The energy gap of aluminum nitride is about 6.2 eV, the highest in all III/V group semiconductor compounds, and this compound is of transmittance, high thermal conductivity, high hardness, thermal resistance, chemical resistance, piezoelectricity, and biocompatibility. Since aluminum nitride has a thermal expansion coefficient approximate to that of silicon, the compound is suitable for a chip package. Accordingly, aluminum nitride is mostly used as a heat sink, an electronic ceramic substrate, a material for an electronic element package, and a surface acoustic wave device.
Current deposition of an aluminum nitride film is conducted via chemical vapor deposition (CVD) or physical vapor deposition (PVD), and the latter is further subdivided into molecular beam epitaxy (MBE), medium frequency magnetron sputtering, and direct current/radio frequency magnetron sputtering. Although physical vapor deposition of an aluminum nitride film is popular and rapid, it is implemented at a high temperature. This results in limiting the selection of a substrate for deposition so as to influence the subsequent application of the film. For example, in the physical vapor deposition described in Taiwan Patent Application NO. 201425631, an aluminum nitride film is formed on a substrate at 400° C. For further example, in the physical vapor deposition described in China Patent Application NO. 102122936, an aluminum nitride film is deposited on a substrate at 830-900° C.
Therefore, there is a need to develop a novel method for physical vapor deposition of an aluminum nitride film, and the method can be implemented at a low temperature to improve the selection of a substrate for deposition.